The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster with an inflatable bladder formed by plastic wall panels that is vented to manage a deflation rate during impact according to the energy at which a passenger impacts the bolster.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions made of various fabrics that emerge from behind various openings upon inflation, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. Pending U.S. patent application publication no. 2012/0267878A1, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes a front wall or panel that faces a vehicle occupant attached to a base wall or panel along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. For example, the base wall may have a pleated (i.e., accordion-like) region that straightens out during inflation. The walls are initially spaced apart by a small amount when in their pre-deployment, non-inflated condition. This allows ingress of the inflation gas in a manner that achieves an even inflation across the panel.
The front and base walls of a typical bladder for an active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but can also be blow molded. When formed separately, the front and base walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation that could result from the high pressures during inflation. The peripheral seal is formed by hot welding, for example.
It is known that in order to optimize the dissipation of energy when an occupant contacts an air bag, inflation gas should be vented to allow a controlled collapse of the airbag that safely decelerates the impacting occupant. Some conventional airbags have utilized vents that only open in response to pressure within the airbag reaching a predetermined threshold. In the case of an active bolster employing a bladder formed by molded plastic panels, it is desirable to vent the inflatable bladder at all times to maintain it at substantially atmospheric pressure during non-crash conditions. Otherwise, noticeable deformation of the interior trim component incorporating the active bolster may occur during temperature extremes since the panel materials are relatively flexible. Furthermore, it is desirable to avoid the use of costly, complicated vent valves of the types known in the prior art.
U.S. patent publication 2012/0248742A1, which is incorporated herein by reference, discloses an active vent for an active bolster wherein the vent has a low flow rate at low pressures and a higher flow rate at higher pressures across the vent. The reduced flow rate of the vent during initial stages of inflation permits the use of a smaller (less costly) inflator, while the higher vent flow rate at higher pressures helps ensure the integrity of the peripheral weld by limiting the pressure rise and avoiding large tearing forces that could cause the seal to fail.
It has been found that an active vent that assumes a higher flow coefficient in response to a higher pressure may lead to insufficient energy management in some circumstances, such as a relatively hard impact (e.g., a relatively heavy passenger moving at a moderate velocity or a smaller passenger moving at a relatively high velocity). In this particular situation, an undesirably fast deflation of the bladder may result in insufficient initial deceleration of the impacting body which may then be followed by a bottoming out of the bolster (and a sudden deceleration of the impacting body) once the bolster has completely collapsed. The present invention overcomes these difficulties while providing an active vent structure with high reliability that can be manufactured using simple, low cost methods.